If the project is shared, you need to add the Shared project to the server project as a Dependency. Then, if the Resource has a Public Modifier, you should be able to access the string using the syntax below:
<Solution>.<Project>.Properties.Rescources.<ResourceName>
If that is not working for you, I would need to have access to your solution to diagnose the issue.
As far as Radzen removing the Resource files, if the solution that Atanas provided does not solve the issue, I am uncertain of a better solution.